Solid state imaging device including a semiconductor substrate on which a plurality of pixel cells have been formed

ABSTRACT

A solid state imaging device including a pixel region where a plurality of pixel cells  10   r   1, 10   g   1 - 10   g   3, 10   b   1 - 10   b   2  . . . have been formed. When focusing on a red pixel cell whose color filter has the longer transmission peak wavelength and a blue pixel cell whose color filter has the shorter transmission peak wavelength, the distribution of substrate contacts is denser in a region in the vicinity of a photodiode in the red pixel cell than a region in the vicinity of a photodiode in the blue pixel cell.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a solid state imaging device includinga semiconductor substrate on which a plurality of pixel cells have beenformed, and in particular to the structure of a pixel region in a MOStype solid state imaging device.

(2) Description of the Related Art

In recent years, MOS type solid state imaging devices have been used asimaging devices in digital still cameras, etc. Each of the MOS typesolid state imaging devices has a pixel region in which a plurality ofpixel cells have been arranged two-dimensionally (for example, arrangedin an array), and a circuit region for driving the pixel cells in thepixel region (Japanese Patent Application Publication No. 2001-230400,and Japanese Patent Application Publication No. 2006-286848). Thefollowing describes the structure of the pixel region in a MOS typesolid state imaging device, with reference to FIG. 1.

As shown in FIG. 1, each pixel cell in the pixel region includes onephotodiode 81 and four transistors (a transfer transistor 82, anamplification transistor 83, a selection transistor 84, and a resettransistor 85). These transistors 81-85 have been formed on a wellregion in a semiconductor substrate. Also, in a pixel region, asubstrate contact (not shown in FIG. 1) has been arranged between pixelcells 80 that are adjacent to each other. The following describes anarrangement of the substrate contact, with reference to FIG. 2. FIG. 2shows six pixel cells in a pixel region 91, namely red pixel cell 80 r1, green pixel cells 80 g 1-80 g 3, and blue pixel cells 80 b 1-80 b 2.

As shown in FIG. 2, the blue pixel cell 80 b 1, the green pixel cell 80g 3, and the blue pixel cell 80 b 2 have been arranged from the top leftin the pixel region 91, and the green pixel cell 80 g 1, the red pixelcell 80 r 1, and the green pixel cell 80 g 2 have been arranged from thebottom left in the pixel region 91.

Note that the red pixel cell 80 r 1 includes a color filter thattransmits red visible light (the wavelength being in the range of 575[nm] to 700 [nm]), each of the green pixel cells 80 g 1-80 g 3 includesa color filter that transmits green visible light (the wavelength beingin the range of 490 [nm] to 575 [nm]), and each of the blue pixel cells80 b 1-80 b 2 includes blue visible light (the wavelength being in therange of 400 [nm] to 490 [nm]).

As shown in FIG. 2, in a MOS type solid state imaging device accordingto a conventional technique, substrate contacts 801-808 have been formedbetween adjacent pixel cells in the pixel region 91. The substratecontacts 801-808 have been formed by evenly spaced from the photodiodes81 r 1, 81 g 1-81 g 3, and 81 b 1-81 b 2 of the pixel cells 80 r 1, 80 g1-80 g 3, and 80 b 1-80 b 2.

As shown in FIG. 2, in the MOS type solid state imaging device, thesubstrate contacts 801 to 808 have been arranged in the pixel region 91,so as to stabilize a well potential. As a result, the transistors 82-85in each of the pixel cells 80 r 1, 80 g 1-80 g 3, and 80 b 1-80 b 2 areoperated at high speed and in a stable manner.

However, the MOS type solid state imaging device having theabove-mentioned substrate contacts has a problem in which a largeshading appears in the output signal due to progress in reducing thesize of image pixels. In particular, shading that appears in the pixelcells 80 b 1 and 80 b 2 is larger than shading that appears in the otherpixel cells, namely the pixel cells 80 r 1 and, 80 g 1-80 g 3, since thepixel cells 80 b 1 and 80 b 2 receive blue visible light having a shortwavelength. The following describes a mechanism of how shading occurs ina MOS type solid state imaging device according to the conventionaltechnique, with reference to FIG. 3.

As shown in FIG. 3, an isolation 901, wirings 902 (902 a, 902 b, and 902c), a color filter 903, and a top lens 904 have been formed in a pixelcell on a semiconductor substrate. Also, a substrate contact 800 hasbeen formed on the semiconductor substrate in a portion corresponding toeach side of the photodiode 81.

A reference number 701 in FIG. 3 shows a boundary (hereinafter referredto as “dividing ridge 701”) where electrons generated by photoelectricconversion are absorbed by the photodiode 81. The electrons generated bythe photoelectric conversion are likely to be concentrated on thephotodiode 81, by repelling the existence of the substrate contact 800.As a result, the dividing ridge 701 spreads toward the substrate contact800, in a shallow area of the semiconductor substrate.

Here, as shown in Japanese National Publication of the TranslatedVersion of PCT Application, No. 2002-513145, a large part of bluevisible light having a short wavelength (400 [nm] to 490 [nm]) isabsorbed by the semiconductor substrate (silicon substrate) at a depthof approximately 0.2 [μm] to 0.5 [μm]. Consequently, as shown in FIG. 3,when the blue visible light enters the semiconductor substrate of a MOStype solid state imaging device according to the conventional technique,electrons are generated in a shallow area of the semiconductor substrateby the photoelectric conversion. Therefore, in a MOS type solid stateimaging device according to the conventional technique, a sensitivitycharacteristic varies depending on a relative positional relationshipbetween the substrate contact 800 and the photodiode 81, whichparticularly have a great impact on the pixel cells 80 b 1 and 80 b 2that receive the incidence of the blue visible light, as describedabove.

Furthermore, shading occurs by a difference in an incident direction ofblue light. In other words, the blue light enters pixels that arepositioned upward (hereinafter referred to as “upper pixels”) in theentirety of a pixel array of a solid state imaging device, in a mannerthat the blue light enters obliquely from a lower direction. Therefore,the photoelectric conversion occurs in an upper portion (in the vicinityof a region where the substrate contacts have been arranged) of thephotodiode in each of the upper pixels, resulting in the upper pixelshaving a high sensitivity. On the contrary, the blue light enters pixelsthat are positioned downward (hereinafter referred to as “lower pixels”)in the entirety of the pixel array of the solid state imaging device, ina manner that the blue light enters obliquely from an upper direction.Therefore, the photoelectric conversion occurs in a lower portion (inthe vicinity of a region having no substrate contact) of the photodiodein each of the lower pixels, resulting in the lower pixels having a lowsensitivity. As described above, shading occurs when a sensitivitydifference occurs between the upper pixels and the lower pixels in thepixel array, due to a difference in the position of each substratecontact with respect to the direction of incident light.

Also, in a solid state imaging device having a multi-pixel one-cellstructure, such as a four-pixel one-cell structure, there are (i) aphotodiode for a blue pixel, the photodiode including the substratecontact arranged in the vicinity thereof and (ii) a photodiode for ablue pixel, the photodiode including the substrate contact not arrangedin the vicinity thereof. This also causes a sensitivity differencebetween the photodiodes in the above-mentioned two pixels.

SUMMARY OF THE INVENTION

The object of the present invention has been achieved in view of theabove-described problem, and an aim thereof is to provide a solid stateimaging device that prevents an occurrence of shading regardless of thewavelength of incident visible light, while ensuring that transistors inpixel cells operate at high speed and in a stable manner, by stabilizingthe reference potential of a substrate.

In order to achieve the above-described aim, the present invention hasthe following structure.

A solid state imaging device according to the present inventioncomprises: a plurality of photodiodes that have been arrangedtwo-dimensionally with spacing between each other, in a semiconductorsubstrate, each of the photodiodes having a function of photoelectricconversion; a plurality of kinds of color filters, each of the colorfilters having been formed above the respective photodiodes andtransmitting light that has, for each kind, a different peak wavelength;and a plurality of substrate contacts that have been respectivelyarranged in vicinity of some or all of the plurality of photodiodes, soas to apply a reference voltage to the semiconductor substrate.

In the solid state imaging device according to the present invention,the plurality of photodiodes include photodiodes that belong to a firstgroup and photodiodes that belong to a second group such that colorfilters above the photodiodes of the first group have a longertransmission peak wavelength, and color filters above the photodiodes ofthe second group have a shorter transmission peak wavelength, and adistribution of the substrate contacts is denser in vicinity of (all of)the photodiodes in the first group than in vicinity of (all of) thephotodiodes in the second group. For example, the solid state imagingdevice of the present invention is characterized in that the substratecontacts have not been formed in the vicinity of the photodiodes in thesecond group, and the plurality of substrate contacts have been formedin the vicinity of the photodiodes in the first group.

In a case where each of the substrate contacts has been formed in thevicinity of the plurality of photodiodes respectively, the substratecontacts in the vicinity of the photodiodes in the second group havebeen arranged closer to each other than the substrate contacts in thevicinity of the photodiodes in the first group.

The present invention may have any structure as long as the relativedistribution density between (i) the substrate contacts that have beenformed in the vicinity of the photodiodes in the first group and (ii)the substrate contacts that have been formed in the vicinity of thephotodiodes in the second group satisfies the above-describedrelationship.

As described above, a solid state imaging device according to thepresent invention includes the substrate contacts that have been formedin a region (pixel region) in which the plurality of photodiodes havebeen arranged two-dimensionally. Therefore, in the solid state imagingdevice according to the present invention, it is possible to apply thereference potential to the semiconductor substrate (including a well),thereby stabilizing the potential (well potential) of the semiconductorsubstrate. As a result, in the solid state imaging device according tothe present invention, the transistors in the pixel cells are operatedat high speed and in a stable manner.

Also, in the solid state imaging device according to the presentinvention, the distribution of the substrate contacts is denser in thevicinity of the photodiodes in the first group than in the vicinity ofthe photodiodes in the second group. As described above, the colorfilters formed above the photodiodes that belong to the first groupselectively transmit light having a peak wavelength that is longer thana peak wavelength of light transmitted by the color filters formed abovethe photodiodes that belong to the second group.

A large part of light having the shorter peak wavelength is absorbed bythe semiconductor substrate at a depth of approximately 0.2 [μm] to 0.5[μm], while light having the longer peak wavelength is absorbed by thesemiconductor substrate at a depth that is deeper than theabove-mentioned depth (see Japanese National Publication of theTranslated Version of PCT Application, No. 2002-513145). As a result,the solid state imaging device according to the present invention is noteasily affected by the above-described dividing ridge that spreads dueto the substrate contacts, compared to a solid state imaging deviceaccording to the above-described conventional technique. This is becausethe distribution of the substrate contacts is dense in the vicinity ofthe photodiodes in the first group in the solid state imaging deviceaccording to the present invention, while the substrate contacts havebeen formed regardless of the peak wavelength of the incident light inthe solid state imaging device according to the conventional technique.

Therefore, in the solid state imaging device according to the presentinvention, it is possible to prevent the occurrence of shadingregardless of the wavelength of the incident visible light, whileensuring high-speed and stable operation of the transistors of the pixelcells, by stabilizing the reference potential of the substrate.

A structure according to the present invention is applicable to a solidstate imaging device having a one-pixel one-cell structure, and is alsoapplicable to a solid state imaging device having a multi-pixel one-cellstructure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and the other objects, advantages and features of the inventionwill become apparent from the following description thereof taken inconjunction with the accompanying drawings which illustrate a specificembodiment of the invention.

In the drawings:

FIG. 1 is a circuit diagram showing the structure of a pixel cell 80 ofa MOS type solid state imaging device according to a conventionaltechnique;

FIG. 2 is a schematic layout showing a relative positional relationshipbetween (i) photodiodes 81 r 1, 81 g 1-81 g 3, and 81 b 1-81 b 2 and(ii) substrate contacts 801-808, in a pixel region 91 of the MOS typesolid state imaging device according to the conventional technique;

FIG. 3 is a sectional diagram schematically showing the structure of thepixel cell 80 in the MOS type solid state imaging device according tothe conventional technique, and an absorption state of electrons e_(r),e_(g), and e_(b) with respect to a photodiode 81;

FIG. 4 is a block diagram showing the structure of a MOS type solidstate imaging device 1 according to embodiment 1;

FIG. 5 is a sectional diagram showing a part of the structure of a pixelcell 10 in the MOS type solid state imaging device 1;

FIG. 6 is a schematic layout showing a relative positional relationshipbetween (i) photodiodes 11 r 1, 11 g 1-11 g 3, and 11 b 1-11 b 2 and(ii) substrate contacts 101-104, in a pixel region 21;

FIG. 7 is a timing chart related to the drive of the MOS type solidstate imaging device 1;

FIG. 8 is a sectional diagram schematically showing the structure of ablue pixel cell 10, and an absorption state of an electron e_(b) withrespect to the photodiode 11 b 1;

FIG. 9 is a sectional diagram schematically showing the structure of oneof a red pixel cell 10 and a green pixel cell 10, and an absorptionstate of an electron e_(r) (e_(g)) with respect to the photodiode 11 r 1(11 g 1);

FIG. 10 is a characteristic diagram showing an optical absorption lengthof light in a silicon substrate, the light being within a visiblespectrum (obtained from Japanese National Publication of the TranslatedVersion of PCT Application, No. 2002-513145);

FIG. 11 is a circuit diagram showing the structure of a pixel cell 40 ina MOS type solid state imaging device according to embodiment 2; and

FIG. 12 is a schematic layout showing a relative positional relationshipbetween (i) photodiodes 11 ba, 11 gb, 11 bc, 41 ga, 41 rb, and 41 gc and(ii) substrate contacts 111-114, in a pixel region 51 of the MOS typesolid state imaging device according to embodiment 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following describes the preferred embodiments for carrying out thepresent invention, with reference to drawings. Note that the followingembodiments are merely examples for the clear and detailed explanationsof the structure of the present invention and the acts/effects achievedfrom the structure. Therefore the present invention shall not be limitedto the embodiments described below, except essential characteristicparts thereof.

Embodiment 1 1. Overall Structure

The following describes the overall structure of a MOS type solid stateimaging device 1 according to the present embodiment, with reference toFIG. 4. The MOS type solid state imaging device 1 shown in FIG. 4 isused as an image input device such as a digital still camera or adigital movie camera.

As shown in FIG. 4, the MOS type solid state imaging device 1 accordingto embodiment 1 includes a pixel region 21 and a periphery circuitportion. The pixel region 21 is formed from a plurality of pixel cells10, and the periphery circuit portion has been arranged on the peripheryof the pixel region 21 so as to drive the pixel cells 10 in the pixelregion 21. The periphery circuit portion includes a vertical scanningcircuit 22, a read circuit 23, a horizontal scanning circuit 24 and aload circuit 25.

The plurality of pixel cells 10, which constitute the pixel region 21,have been arranged two-dimensionally in a semiconductor substrate. Notethat, although the semiconductor substrate is not shown in FIG. 4, adirection along the main surface of the semiconductor substratecorresponds to a direction along the paper surface.

As shown in a portion surrounded by a chain double-dashed line in FIG.4, each of the pixel cells 10 is an amplification-type unit pixel, andhas a circuit configuration identical to each other. Each of the imagepixel cells 10 includes a photodiode 11 and four transistors (a transfertransistor 12, an amplification transistor 13, a selection transistor14, and a reset transistor 15), etc.

Between each of the image pixels 10 arranged in the horizontal directionof FIG. 4, the gate electrodes of the transfer transistors 12 areconnected to each other by a wiring line L1, the gate electrodes of thereset transistors 15 are connected to each other by a wiring line L2,and the gate electrodes of the selection transistors 14 are connected toeach other by a wiring line L3. Also, between each of the image pixels10 arranged in the vertical direction of FIG. 4, the sources of theselection transistors 14 are connected to each other by a wiring lineL4.

The photodiodes 11 is a device portion having a photoelectric conversionfunction that generates signal charge in accordance with intensity ofincident light received by the corresponding pixel cell 10. Note thatone end of the photodiode 11 is grounded, and another end thereof isconnected to a source of the transfer transistor 12. The transfertransistor 12 is a device portion for transferring, to a drain thereof,the signal charge generated with use of the photoelectric conversionfunction of the photodiode 11. The drain of the transmission transistor12 functions as a detection unit, and is connected to the gate electrodeof the amplification transistor 13 and the source of the resettransistor 15. Note that one of the drain of the transfer transistor 12and an extended portion of the transfer transistor 12 is a floatingdiffusion FD.

The reset transistor 15 is a device portion for resetting the signalcharge accumulated in the floating diffusion FD in a predeterminedcycle. A drain of the reset transistor 15 is electrically connected topower supply voltage VDD. The amplification transistor 13 is a deviceportion for outputting the signal charge accumulated in the floatingdiffusion FD in accordance with a signal from the vertical scanningcircuit 22, etc., when the selection transistor 14 is turned on. A drainof the amplification transistor 13 is connected to the power supplyvoltage VDD, and a source of the amplification transistor 13 isconnected to a drain of the selection transistor 14.

In the four transistors, namely transistors 12-15 in the pixel cell 10,the amplification transistor 13 performs an amplification function ofthe signal charge, and the other transistors 12, 14-15 each perform aswitching function.

Note that although not shown in FIG. 4, each pixel cell 10 has a colorfilter 203 and a top lens 204. The color filters 203 include red colorfilters, green color filters, and blue color filters, and have beenformed above the photodiodes 11. Also, each of the top lenses 204 hasbeen formed on the color filter 203 of the respective color pixel cells10 (see FIGS. 8 and 9). Also, in the MOS type solid state imaging device1, a plurality of substrate contacts have been formed in the pixelregion 21, so as to apply a reference potential (for example, 0 [V]) tothe semiconductor substrate (now shown), which is described below.

2. Structure of Peripheral Region of Photodiode 11 in Each Pixel Cell 10

The following describes a structure in a peripheral region of thephotodiode 11 in each pixel cell 10 in the MOS type solid state imagingdevice 1, with reference to FIG. 5.

As shown in FIG. 5, in the MOS type solid state imaging device 1according to embodiment 1, the photodiode 11, the transfer transistor12, and the floating diffusion FD have been formed from left to right ineach pixel cell 10. The photodiode 11 includes a p-type doped region 11p and an n-type doped region 11 n. The p-type doped region 11 p has beenformed on the upper portion of the photodiode 11, and the n-type dopedregion 11 n has been formed on the lower portion of the photodiode 11.The reference number 12 g denotes a gate of the transfer transistor 12.

In the MOS type solid state imaging device 1, the n-type doped region 11n in the photodiode 11 has been extended to a region located below thegate 12 g of the transfer transistor 12.

The MOS type solid state imaging device having the above-describedstructure transfers all the signal charge generated in the photodiode 11to the floating diffusion FD when reading data, compared to a case wherethe MOS type solid state imaging device does not have the structure inwhich the n-type doped region 11 n has been extended to the regionlocated below the gate 12 g of the transfer transistor 12.

3. Substrate Contacts 101-104

The following describes a relative positional relationship between (i)photodiodes 11 r 1, 11 g 1-11 g 3, and 11 b 1-11 b 2 and (ii) substratecontacts 101-104, in the pixel region 21, with reference to FIG. 6. FIG.6 schematically shows six pixel cells that have been extracted, namely10 r 1, 10 g 1-10 g 3, and 10 b 1-10 b 2. In the six pixel cells, thephotodiodes 11 r 1, 11 g 1-11 g 3, and 11 b 1-11 b 2, and the substratecontacts 101-104 are only shown.

In the pixel cell 10 r 1, the red color filter 203 (see FIGS. 8 and 9)has been provided above the photodiode 11 r 1. The photodiode 11 r 1receives red visible light having a peak wavelength in the range of 575[nm] to 700 [nm] inclusive.

Also, in the pixel cells 10 g 1-10 g 3, each of the green color filters203 (see FIGS. 8 and 9) has been provided above the photodiodes 11 g1-11 g 3, respectively. The photodiodes 11 g 1-11 g 3 receive greenvisible light having a peak wavelength in the range of 490 [nm] to 575[nm] inclusive. Likewise, in the pixel cells 10 b 1-10 b 2, each of theblue color filters 203 (see FIGS. 8 and 9) has been provided above thephotodiodes 11 b 1-11 b 2, respectively. The photodiodes 11 b 1-11 b 2receive blue visible light having a peak wavelength in the range of 400[nm] to 490 [nm] inclusive.

As shown in FIG. 6, in the MOS type solid state imaging device 1according to embodiment 1, the substrate contacts 101-104 have beenformed so as to be adjacent to the pixel cells 10 g 1, 10 r 1 and 10 g 2in the pixel region 21. However, no substrate contact has been formed inportions that are adjacent to the pixel cells 10 b 1 and 10 b 2, whichhave been arranged in the upper portion in the Y-axial direction of FIG.6.

The substrate contacts 102 and 103 have been formed so as to be closerto the pixel cell 10 r 1. In other words, the substrate contact 102 hasbeen arranged so as to be closer to the photodiode 11 g 1 than thephotodiode 11 r 1. Here, the photodiode 11 g 1 is in the pixel cell 10 g1 that is located on the left side of the substrate contact 102, and thephotodiode 11 r 1 is in the pixel cell 10 r 1 that is located on theright side of the substrate contact 102.

Also, as shown in FIG. 6, the substrate contacts 101-104 have beenformed on a line L that is a line connecting the center points, in theY-axial direction, of the photodiodes 11 r 1 and 11 g 1-11 g 2 in thepixel cells 10 r 1 and 10 g 1-10 g 2. With a structure as describedabove, the substrate contacts 101-104 are symmetrically arranged in theY-axial direction, with respect to the photodiodes 11 r 1, and 11 g 1-11g 2. As a result, the MOS type solid state imaging device 1 preventsvariation in the sensitivity characteristic in the entirety of the pixelregion 21, even in the incident direction of light.

4. Drive of MOS Type Solid State Imaging Device 1

The following outlines the drive of the MOS type solid state imagingdevice 1, with reference to FIG. 7.

In FIG. 7, a pulse ØRS is a control pulse for the on/off control of thereset transistor 15. Also, a pulse ØSEL is a control pulse for theon/off control of the selection transistor 14, and a pulse ØTG is apulse for the on/off control of the transfer transistor 12.

As shown in FIG. 7, a High level control pulse ØRS is applied to thegate of the reset transistor 15 in a selected one of the pixel cells 10on one horizontal line. As a result, the reset transistor 15 in theselected pixel cell 10 is turned on (timing t1).

Then, the control pulse ØRS is set to a Low level, so as to turn off thereset transistor 15 (timing t2). Subsequently, a High level controlpulse ØSEL is applied to the gate of the selection transistor 14 in thepixel cell 10 (timing t3), so as to turn on the selection transistor 14.When the selection transistor is turned on, the potential of the wiringline L4 is stored in the read circuit 23.

Then, a High level control pulse ØTG is applied to the gate of thetransfer transistor 12 (timing t4), so as to turn on the transfertransistor 12. When the transfer transistor 12 is turned on, electriccharge that has been generated and accumulated by the photoelectricconversion in the photodiode 11 passes through the floating diffusion FDand is transferred to the gate of the amplification transistor 13.

The electric charge transferred to the gate of the amplificationtransistor 13 is converted into voltage information by the parasiticcapacity, and is read to the wiring line L4 via the amplificationtransistor 13 and the selection transistor 14. The read circuit 23outputs a difference between read data that has been converted into thevoltage information and a pre-stored signal level.

After the above-described signal output process has been completed, thecontrol pulse ØSEL and the control pulse ØTG are sequentially set to theLow level (timing t5 and t6).

5. Superiority of MOS Type Solid State Imaging Device 1

The following describes the superiority of the MOS type solid stateimaging device 1 according to embodiment 1, with reference to FIGS. 8 to10. FIG. 8 is a sectional diagram schematically showing the structure ofthe blue pixel cell 10, and an absorption state of an electron e_(b)with respect to the photodiode 11 b 1, and FIG. 9 is a sectional diagramschematically showing the structure of one of the red pixel cell 10 andthe green pixel cell 10, and an absorption state of an electron e_(r)(e_(g)) with respect to the photodiode 11 r 1 (11 g 1).

The MOS type solid state imaging device 1 according to embodiment 1includes the plurality of substrate contacts 101-104, . . . that havebeen formed in the pixel region 21. The plurality of substrate contacts101-104, . . . are used to set the potential (well potential) of thesemiconductor substrate to a reference potential (for example, 0 [V]).This stabilizes the potential (well potential) of the semiconductorsubstrate of the MOS type solid state imaging device 1, therebyoperating the transistors 12-15 in each pixel cell 10 at high speed andin a stable manner.

As shown in FIG. 8, isolations 201 have been formed in a region in thevicinity of the blue pixel cell 10, so as to surround both sides of theupper portion of the photodiode 11 b 1. Then, without providing anysubstrate contacts, wiring lines 202 (wiring layers 202 a, 202 b, and202 c), a color filter 203, and a top lens 204 have been formed aboveeach of the isolations 201.

As shown in FIG. 9, the isolations 201 have been formed in a region inthe vicinity of one of the red pixel cell 10 and the green pixel cell10, so as to surround both sides of the upper portion of the photodiode11 r 1 (11 g 1). Then, a substrate contact 100 (equivalent to 101-104, .. . ) is provided so as to be sandwiched between each of the isolations201. Each of the substrate contacts 100 is connected to the wiring layer202 a, and receives a reference potential via the wiring layer 202 a.

In other words, in the MOS type solid state imaging device 1, thedistribution of the substrate contacts 100 is denser in the regions thatare in the vicinity of the photodiode 11 r 1 (11 g 1) in the red pixelcell 10 and the green pixel cell 10, than the region that is in thevicinity of the photodiode 11 b 1 in the blue pixel cell 10.

As described above, in the MOS type solid state imaging device 1according to embodiment 1, the substrate contacts 100 have been formedin the region that is in the vicinity of one of the red pixel cell 10and the green pixel cell 10, and not in the region in the vicinity ofthe blue pixel cell 10. With this structure, the dividing ridge(boundary where electrons generated by photoelectric conversion areabsorbed by the photodiode 11 b 1) does not spread even along thesubstrate surface in the blue pixel cell 10, as shown in FIG. 8. As aresult, although blue light having a wavelength in the range in of 400[nm] to 490 [nm] is photoelectrically converted in a region that isshallow (approximately in the range of 0.2 [μm] to 0.5 [μm] inclusive)from the substrate surface, the electrons e_(b) generated in theperipheral region of the photodiode 11 b 1 in the blue pixel cell 10 arenot concentrated on the photodiode 11 b 1, since no substrate contact isprovided in the vicinity of the blue pixel cell 10.

Here, as shown in FIG. 10 (cited from Japanese National Publication ofthe Translated Version of PCT Application, No. 2002-513145), a largepart of blue light having a peak wavelength in the range of 400 [nm] to490 [nm] inclusive is absorbed by the semiconductor substrate at a depthof approximately 0.2 [μm] to 0.5 [μm].

On the other hand, a large part of green light having a peak wavelengthin the range of 490 [nm] to 575 [nm] inclusive is absorbed by thesemiconductor substrate at a depth of approximately 0.5 [μm] to 1.5[μm], and a large part of red light having a peak wavelength in therange of 575 [nm] to 700 [nm] inclusive is absorbed by the semiconductorsubstrate at a depth of approximately 1.5 [μm] to 3.0 [μm].

Therefore, the MOS type solid state imaging device 1 prevents blue lightfrom being excessively concentrated on the photodiode 11 b 1 in ashallow region of the substrate, by not providing any substrate contact100 in the vicinity of the photodiode 11 b 1 in the blue pixel cell 10.

Also, as shown in FIG. 6, in the MOS type solid state imaging device 1,the substrate contacts 101-104 have been formed on the positionscorresponding to the center points of the photodiodes 11 r 1 and 11 g1-11 g 2 in the Y-axial direction. In other words, the substratecontacts 101-104 have been arranged on the virtual line L that passesbetween the centers of the photodiodes 11 r 1 and 11 g 2. Therefore,even in the red and green pixel cells 10, the effects of the substratecontacts 101-104 on the photodiodes 11 g 1, 11 r 1, and 11 g 2 areequalized at least along the Y-axial direction.

Furthermore, as shown in FIG. 6, the substrate contact 102 is notarranged midway between the photodiode 11 g 1 and the photodiode 11 r 1,and the substrate contact 103 is not arranged midway between thephotodiode 11 r 1 and the photodiode 11 g 2. Instead, each of thesubstrate contacts 102 and 103 is arranged so as to be closer to the redpixel cell 10 r 1. This makes it possible to further reduce the effectsof the substrate contacts 102 and 103 on the green pixel cells 10 g 1and 10 g 2 that each receive green light whose wavelength is shorterthan red light.

With the above-described structure, the MOS type solid state imagingdevice 1 according to embodiment 1 ensures high speed and stableoperation of the transistors 12-15 in each pixel cell 10, with thesubstrate contacts 101-104 formed therein, and also prevents theoccurrence of shading with the arrangement of the substrate contacts101-104. This technique is useful when further reducing the size of eachpixel cell.

Embodiment 2

The following describes the structure of a MOS type solid state imagingdevice according to embodiment 2, with reference to FIGS. 11 and 12.Note that each of FIGS. 11 and 12 shows some of pixel cells 40 (40 a, 40b, and 40 c) in a pixel region 51. The rest of the structure of the MOStype solid state imaging device according to embodiment 2 is basicallythe same as that of the MOS type solid state imaging device 1 accordingto embodiment 1 described above.

As shown in FIG. 11, two photodiodes, namely photodiodes 11 and 41 havebeen formed in each of the pixel cells 40, in the MOS type solid stateimaging device according to embodiment 2. Also, transfer transistors 12and 42 have been formed with respect to the photodiodes 11 and 41 ineach pixel cell 40. The rest of the structure of each pixel cell 40 isthe same as that of each pixel cell 10.

As shown in FIG. 12, when three pixel cells, namely pixel cells 40 a, 40b, and 40 c are seen by being extracted from the pixel region 51, thepixel cells 40 a, 40 b, and 40 c have been arranged in the direction ofrows. In the pixel cell 40 a, a photodiode 11 ba for blue light and aphotodiode 41 ga for green light have been formed as a pair. Thephotodiode 11 ba and the photodiode 41 ga are connected to a transfertransistor 12 a and a transfer transistor 42 a, respectively, and sharean amplification transistor 13 a, a selection transistor 14 a, and areset transistor 15 a.

In the same manner, a photodiode 11 gb for green light and a photodiode41 rb for red light have been formed as a pair in the pixel cell 40 b,and a photodiode 11 bc for blue light and a photodiode 41 gc for greenlight have been formed as a pair in the pixel cell 40 c.

As shown in FIG. 12, in the pixel region 51 of the MOS type solid stateimaging device according to embodiment 2, substrate contacts 111-114have been formed in the vicinity of the photodiodes 41 ga, 41 rb, and 41gc that have been arranged in a lower row of the pixel cells 40 a, 40 b,and 40 c, whereas no substrate contact has been formed in the vicinityof the photodiodes 11 ba, 11 gb, and 11 bc that have been arranged in anupper row of the pixel cells 40 a, 40 b, and 40 c. Note that thesubstrate contacts 111-114 are different from those in the MOS typesolid state imaging device 1 according to the above-described embodiment1, in that the substrate contacts 111-114 have not been formed on a lineconnecting the center points of the photodiodes 41 ga, 41 rb, and 41 gcin the lower row. However, it is of course possible to arrange thesubstrate contacts 111-114 on the line connecting the center points, bydevising the arrangement of the reset transistors 15 a, 15 b and 15 c,in the same manner as the above-described embodiment 1.

As described above, the MOS type solid state imaging device according toembodiment 2 adopts a so-called two-pixel one-cell structure, andachieves the same advantageous effect as the MOS type solid stateimaging device 1 according to the above-described embodiment 1, byadopting the arrangement of the substrate contacts 111-114 shown in FIG.12. In other words, the MOS type solid state imaging device according toembodiment 2 also effectively prevents shading, while ensuring highspeed and stable operation of the transistors 12-15 and 42 in the pixelcell 40.

Note that, in the MOS type solid state imaging device according toembodiment 2, the substrate contacts 111-114 have not been arrangedadjacent to the transfer transistors 42 a, 42 b, and 42 c in each of thepixel cells 40 a, 40 b, and 40 c. Instead, the reset transistors 15 a,15 b, and 15 c have been arranged between the substrate contacts 111-114and the transfer transistors 42 a, 42 b, and 42 c, as shown in FIG. 12.Therefore, in the MOS type solid state imaging device according toembodiment 2, it is possible to minimize a difference in the sensitivitycharacteristic between each pair of photo diodes in the respective pixelcells 40 a, 40 b, and 40 c, namely between the photodiodes 11 ba and 41ga in the pixel cell 40 a, the photodiodes 11 gb and 41 rb in the pixelcell 40 b, and the photodiodes 11 bc and 41 gc in the pixel cell 40 c.

In other words, the MOS type solid state imaging device according toembodiment 2 also adopts the structure as shown in FIG. 5, in which then-type doped region 11 n in the photodiode 11 (41) has been extended tothe region located below the transfer transistor 12 (42). Therefore, ifthe substrate contacts 111-114 have been arranged adjacent to thetransfer transistors 42, a difference in the sensitivity characteristicis likely to occur between each pair of photodiodes 11 ba and 41 ga, thephotodiodes 11 gb and 41 rb, and the photodiodes 11 bc and 41 gc, due tothe influence of the substrate contacts 111-114.

On the other hand, as shown in FIG. 12, in the MOS type solid stateimaging device according to embodiment 2, the reset transistors 15 a, 15b, and 15 c have been arranged between the transfer transistors 42 a, 42b, and 42 c and the substrate contacts 111-114, thereby minimizing adifference in the sensitive characteristic between each pair ofphotodiodes 11 ba and 41 ga, the photodiodes 11 gb and 41 rb, and thephotodiodes 11 bc and 41 gc. The structure in which the resettransistors have been arranged in between can be adopted for theabove-described solid state imaging device 1 according to embodiment 1that has the one-pixel one-cell structure. In this case, it is alsopossible to achieve an advantageous effect of suppressing the effect ofthe substrate contacts on the transfer transistors.

Note that devices that have been arranged between the substrate contacts111-114 and the transfer transistors 42 a, 42 b, and 42 c are notlimited to the reset transistors 15 a, 15 b, and 15 c. Instead, it ispossible to use devices other than the reset transistors 15 a, 15 b, and15 c.

<Supplementary Remarks>

In the above-described embodiments 1 and 2, the substrate contacts110-104 and 111-114 have not been arranged in the vicinity of thephotodiodes 11 b 1 and 11 b 2 in the blue pixel cells 10, or thephotodiodes 11 ba and 11 bc in the blue pixel cells 40. However, it isnot the intention of the present invention that the substrate contactsshould not be arranged in the vicinity of the photodiodes in the bluepixel cells. In the present invention, it is acceptable as long as thedistribution of the substrate contacts is denser in the vicinity of thered and green pixel cells (the substrate contacts in the vicinity of thephotodiodes in a first group) than the substrate contacts in thevicinity of in the blue pixel cells (the substrate contacts in thevicinity of the photodiodes in a second group). Here, color filtersabove the photodiodes in the first group have the longer transmissionpeak wavelength, and color filters above the photodiodes in the secondgroup have the shorter transmission peak wavelength.

Also, one example used in the above-described embodiment 2 is the MOStype solid state imaging device including the pixel region 51 that has atwo-pixel one-cell structure. However, the present invention can ofcourse be applied to a MOS type solid state imaging device that has amulti-pixel one-cell structure, such as a four-pixel one-cell structureor a six-pixel one-cell structure. Note that, in a case where thepresent invention is applied to the MOS type solid state imaging devicethat has a multi-pixel one-cell structure, it is not always necessary toshare the diffusion part for the drains of transfer transistors, asshown in embodiment 2. Instead, each of the diffusion parts may beprovided for the respective transfer transistors, so as to beelectrically connected to the shared amplification transistor.

Also, the above-described embodiments 1 and 2 adopted, as one example,the structure where the plurality of pixel cells 10 and 40 have beenarranged in a matrix (array). However, the present invention may beapplied to a MOS type solid state imaging device that has a structurewhere a plurality of pixel cells have been arranged in a honeycombpattern.

In the above-described embodiments 1 and 2, a primary-color filter isassumed to be used as the color filter 203. However, it is possible touse a complementary-color filter or a multilayer interference filterinstead.

Also, FIG. 12 shows three pixel cells in one row, namely the pixel cells40 a, 40 b, and 40 c. However, more pixel cells of course exist in theupward and downward directions of the pixel cells 40 a, 40 b, and 40 c.In this case, the arrangement of each pair of photodiodes in therespective pixel cells in each row may be flipped upside down, so thatthe spacing between the substrate contacts 111-114 and the photodiodesof the blue pixel cells is greater than the spacing between thesubstrate contacts 111-114 and the photodiodes of the other pixel cells.In this way, the spacing between the substrate contact and thephotodiode having the blue color filter is larger than the spacingbetween the substrate contact and the photodiode having one of the redand green color filters, even among the pixel cells belonging to thesame column.

Also, the structure according to the present invention may be adopted toa solid state imaging device having a one-pixel one-cell structure and asolid state imaging device having a multi-pixel one-cell structure, aswell as the solid-state imaging devices according to the above-describedembodiments 1 and 2. In this case, it is also possible to achieve thesame effect as described above.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to be notedthat various changes and modifications will be apparent to those skilledin the art. Therefore, unless such changes and modifications depart fromthe scope of the present invention, they should be construed as beingincluded therein.

1. A solid state imaging device comprising: a plurality of photodiodesthat have been arranged two-dimensionally with spacing between eachother, in a semiconductor substrate, each of the photodiodes having afunction of photoelectric conversion; a plurality of kinds of colorfilters, each of the color filters having been formed above therespective photodiodes and transmitting light that has, for each kind, adifferent peak wavelength; a plurality of substrate contacts that havebeen respectively arranged in vicinity of some or all of the pluralityof photodiodes, so as to apply a reference voltage to the semiconductorsubstrate, wherein the plurality of photodiodes include photodiodes thatbelong to a first group and photodiodes that belong to a second groupsuch that color filters above the photodiodes of the first group have alonger transmission peak wavelength, and color filters above thephotodiodes of the second group have a shorter transmission peakwavelength, and a distribution of the substrate contacts is denser invicinity of the photodiodes in the first group than in vicinity of thephotodiodes in the second group.
 2. The solid state imaging device ofclaim 1, wherein a region where the plurality of photodiodes have beenarranged two-dimensionally includes a portion where a first photodiodeis adjacent to a second photodiode, the first photodiode being one ofthe photodiodes that belongs to the first group, the second photodiodebeing one of the photodiodes that belongs to the second group, one ofthe plurality of substrate contacts having been formed between the firstphotodiode and the second photodiode, and in the portion, the one of thesubstrate contacts has been formed so as to be closer to the firstphotodiode than the second photodiode.
 3. The solid state imaging deviceof claim 1, wherein a region where the plurality of photodiodes havebeen arranged two-dimensionally includes a portion where at least threeof the substrate contacts have been formed, and the at least three ofthe substrate contacts have been formed at a constant pitch.
 4. Thesolid-state imaging device of claim 1, wherein in correspondence witheach of the photodiodes, a transfer transistor has been formed, a sourceof which is connected to one end of the photodiode, an amplificationtransistor has been formed that is connected to a drain of the transfertransistor, and amplifies a potential of the drain, a reset transistorthat initializes a potential level of the drain in the transfertransistor, and in a portion where one of the substrate contacts hasbeen formed in vicinity of one of the photodiodes, either theamplification transistor or the reset transistor has been formed betweenthe one of the substrate contacts and the one of the transfertransistors.
 5. The solid-state imaging device of claim 1, wherein aregion where the plurality of photodiodes have been arrangedtwo-dimensionally includes pixel cells each having two or more of thephotodiodes that are adjacent to each other, each of the pixel cellsincludes two or more transfer transistors, an amplification transistor,and a reset transistor, the two or more transfer transistorscorresponding to the two or more photodiodes respectively, including asource connected to one end of each of the two or more photodiodes, andsharing a drain, the amplification transistor connected to the drain ofthe two or more transfer transistors, and amplifying a potential of thedrain, the reset transistor initializing a potential level of the drainof the two or more transfer transistors, and in a portion where one ofthe substrate contacts has been formed in vicinity of one of thephotodiodes, either the amplification transistor or the reset transistorhas been formed between (i) the one of the substrate contacts and (ii)the two or more transfer transistors.
 6. The solid state imaging deviceof claim 1, wherein the photodiodes that belong to the first groupreceive, via the color filters formed thereabove, light having a peakwavelength in a range of 575 nm to 700 nm inclusive, and the photodiodesthat belong to the second group receive, via the color filters formedthereabove, light having a peak wavelength in a range of 400 nm to 490nm inclusive.